class_docstr: Traitlet class storing a JupyterChart's selections
code: def _set_value(self, key, value):
      self.unobserve(self._make_read_only, names=key)
      setattr(self, key, value)
      self.observe(self._make_read_only, names=key)
  
imports: import json
  import anywidget
  import traitlets
  import pathlib
  from typing import Any, Set, Optional
  import altair
  from altair.utils._vegafusion_data import using_vegafusion, compile_to_vegafusion_chart_state
  from altair import TopLevelSpec
  from altair.utils.selection import IndexSelection, PointSelection, IntervalSelection
label_desc: Use image node_id 4 for calling the Selections obj's underlying member method code with example usage: obj._set_value(key, value) without return types